Thrombin converts singlet oxygen (1O2)-oxidized fibrinogen into a soluble t-PA cofactor. A new method for preparing a stimulator for functional t-PA assays.

Activated phagocytes, particularly polymorphonuclear leukocytes (neutrophils), by means of oxidative photonic burst, i.e., the combined activation of NADPH-oxidase and myeloperoxidase, generate large amounts of oxidants of the hypochlorite/chloramine type that are an important physiologic source for the nonradical, photon-emitting oxidant singlet oxygen (1O2), which (in the dark blood stream) is both a signal and an agent of defense against bacteria or fibrin. 1O2-oxidized fibrinogen or oxidized fibrin monomer has previously been shown to be unpolymerizable, and methionine to methionine sulfoxide-oxidized fibrinogen occurs in circulating blood. The present study demonstrates that thrombin converts oxidized fibrinogen into a soluble stimulator of tissue-type plasminogen activator (t-PA). After addition of 0.1 IU thrombin to 25 microl oxidized normal human plasma and an incubation time of 10 min (room temperature), t-PA activity increases about 20-fold when compared with oxidized plasma without the addition of thrombin. Thus, since oxidized fibrin monomer is a t-PA cofactor, thrombin-degraded oxidized fibrinogen can be used as a stimulator in functional t-PA assays.